Wind turbines are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. Generally, a wind turbine converts kinetic energy from the wind into mechanical energy and then subsequently converts the mechanical energy into electrical power. A horizontal-axis wind turbine includes a tower, a nacelle located at the apex of the tower, and a rotor that is supported in the nacelle. The rotor is coupled either directly or indirectly with a generator, which is housed inside the nacelle. The rotor includes a central hub and a plurality of blades (e.g., three blades) mounted thereto and extending radially therefrom.
Modern wind turbines are massive structures and are generally assembled in pieces. In this regard, many off-shore wind turbines have their various components delivered quay side for subsequent delivery to the off-shore installation site. Some installation procedures may call for some amount of assembly quay side resulting in a number of sub-assemblies. For example, the wind turbine tower, which may be formed by a number of tower sections, may be assembled quay side for delivery to an off-shore installation site. The nacelle may also be delivered quay side in a complete or nearly-completed form. Alternatively, some assembly of the nacelle may also be performed quay side resulting in a complete or nearly complete nacelle. Lastly, the blades, themselves being quite massive in size, may be delivered quay side for subsequent delivery to the off-shore installation site.
These various sub-assemblies, e.g., the tower, nacelle, and blades, are then loaded onto a vessel and transported to the installation site for final assembly. In this regard, suitable hoisting devices, such as cranes, winches, hoists, or the like, are located quay side and used to load the wind turbine sub-assemblies on board the vessel. To this end, the hoisting device typically includes a cable arrangement having a hook or other hoisting connector which couples with the wind turbine sub-assemblies for moving the sub-assemblies onto the vessel. However, because of the vast differences in the geometry of the wind turbine sub-assemblies (e.g., shape, size, etc.), the manner in which the sub-assemblies couple to the hook of the hoisting device may differ.
By way of example, to load a wind turbine tower onto a vessel, a tower lifting yoke is coupled to one end of the tower. The tower lifting yoke is a beam-like member which is generally bolted to an end of the assembled tower and includes two eyelets on opposed ends of the beam. Cables then extend from the eyelets to the hook of the hoisting device so that the tower may be lifted by the hoisting device and loaded onto the vessel. As the time and labor involved in coupling a tower lifting yoke to a tower may be appreciable, numerous lifting yokes are kept on hand so that each tower being transported to the installation site may have its own dedicated lifting yoke, thereby expediting the loading process of the towers onto the vessel. Once the towers are loaded onto the vessel, the lifting yokes are not removed, but remain with the towers so as to provide an interface for a hoisting device at the installation site. For example, the tower lifting yoke may be used to interface with an installation site hoisting device to unload the tower or position the tower at the installation site for final assembly.
In regard to the nacelle, another separate device is typically provided that couples to the hook of the hoisting device for loading the nacelle onto the vessel. Thus, after the towers are loaded onto the vessel, for example, the working crew couples a nacelle lifting yoke to the hoisting device. The nacelle lifting yoke is an elongate cylindrical member with trunnions at opposed ends thereof. Cables extend from the trunnions to eyelets on the nacelle. Unlike the tower lifting yoke, however, each nacelle does not have its own dedicated yoke. Instead, a single nacelle lifting yoke may be used to load the nacelles on board the vessel. After the nacelles have been loaded on board the vessel, the nacelle lifting yoke is uncoupled from the hoisting device. The nacelle lifting yoke may be stored either on board the vessel, or stored quay side if, for example, there is another nacelle lifting yoke at the installation site.
To load the blades on board the vessel, yet another device may be used to interface with the hoisting device. For transport of wind turbine blades, frame members are typically coupled to the blades that facilitate their loading and stacking on, for example, the vessel. By way of example, a root frame member and a tip frame member may be coupled to each blade at the quay side, and several frame members stacked on top of each other to form a frame assembly. A relatively large blade lifting yoke is then coupled to the hook of the hoisting device via suitable cables. The blade lifting yoke includes a spreader bar that couples to the frame assembly so that the blades may be lifted by the hoisting device and loaded onto the vessel. Similar to the towers, as the time and labor involved in coupling the frame members to a blade may be appreciable, numerous frame members are kept on hand so that each blade being transported to the installation site may have its own dedicated frame member, and thereby expedite the loading process of the blades onto the vessel. Once the blades are loaded onto the vessel, the frame members are not removed, but remain with the blades to facilitate, for example, stacking of the blades on board the vessel or unloading the blades at the installation site.
With the vessel loaded with the various wind turbine sub-assemblies, the vessel moves to the installation site where the sub-assemblies are finally assembled to form the wind turbine. In this regard, the installation site typically includes a hoisting device, such as a crane, winch, hoist, or the like, having a cable arrangement and hook or other hoisting connector configured to couple with the wind turbine sub-assemblies. Similar to the loading process, due to the vast differences in geometry and the task being performed, the manner in which the sub-assemblies couple to the hook of the installation site hoisting device may differ.
In this regard, and as noted above, the tower lifting yokes used to load the towers remain with the towers during transport such that these lifting yokes may again be used to unload or position the towers for final assembly. Afterward, the hook may be uncoupled from the tower lifting yoke. Once the tower is erected during installation, the lifting yoke may be removed from the tower. The nacelle lifting yoke may then be coupled to the hook of the hoisting device for unloading or positioning the nacelle for final assembly. As noted above, the nacelle lifting yoke may be the one stored on board the vessel or one that was previously located at the installation site. In any event, afterward, the hook may be uncoupled from the nacelle lifting device. Lastly, if the blades are being unloaded at the installation site, the hook of the hoisting device may be coupled to a blade lifting yoke and unloaded from the vessel in a manner similar to that above. Alternatively, if the blades are being assembled to the wind turbine from the vessel, a blade gripping tool may be coupled to the hook of the hoisting device. The blade gripping tool provides a secure coupling to the blade as the blade is being lifted by the hoisting device for assembly to the hub of the wind turbine rotor. After the blades are coupled to the hub, the blade gripping tool may be uncoupled from the hook of the hoisting device.
The process described above, which is typical for many off-shore wind turbine installations, has several drawbacks. For example, each sub-assembly includes its own specific connection device for coupling with the hook or hoisting connector of the hoisting device, i.e., the tower has the tower lifting yoke, the nacelle has the nacelle lifting yoke, and the blades have a blade lifting yoke and blade gripping tool. Attaching and removing the current tower lifting yokes is labor intensive, time consuming, and requires numerous units. Additionally, when transitioning from the loading or assembly of one sub-assembly to another sub-assembly, the hoisting device goes through a part or equipment change out and add on. For example, to load or assemble the nacelle, the nacelle lifting yoke must be coupled to the hook and then de-coupled from the hook upon completion so that, for example, the blades may be unloaded or assembled. These change-out processes are time consuming and present safety considerations for the workers or crew members responsible for loading, unloading, and assembly of the wind turbine sub-assemblies.
Thus, there is a need for an improved method and apparatus for handling wind turbine components during, for example, loading processes, unloading processes, and/or assembly processes that overcome these various drawbacks.